ttoul.3

This a good VPN source

.TH IPSEC_TTOUL 3 "16 Aug 2000"
.\" RCSID $Id: ttoul.3,v 1.3 2004/04/09 18:00:37 mcr Exp $
.SH NAME
ipsec ttoul, ultot \- convert unsigned-long numbers to and from text
.SH SYNOPSIS
.B "#include <freeswan.h>
.sp
.B "const char *ttoul(const char *src, size_t srclen,"
.ti +1c
.B "int base, unsigned long *n);"
.br
.B "size_t ultot(unsigned long n, int format, char *dst,"
.ti +1c
.B "size_t dstlen);"
.SH DESCRIPTION
.I Ttoul
converts a text-string number into a binary
.B "unsigned long"
value.
.I Ultot
does the reverse conversion, back to a text version.
.PP
Numbers are specified in text as
decimal (e.g.
.BR 123 ),
octal with a leading zero (e.g.
.BR 012 ,
which has value 10),
or hexadecimal with a leading
.B 0x
(e.g.
.BR 0x1f ,
which has value 31)
in either upper or lower case.
.PP
The
.I srclen
parameter of
.I ttoul
specifies the length of the string pointed to by
.IR src ;
it is an error for there to be anything else
(e.g., a terminating NUL) within that length.
As a convenience for cases where an entire NUL-terminated string is
to be converted,
a
.I srclen
value of
.B 0
is taken to mean
.BR strlen(src) .
.PP
The
.I base
parameter of
.I ttoul
can be
.BR 8 ,
.BR 10 ,
or
.BR 16 ,
in which case the number supplied is assumed to be of that form
(and in the case of
.BR 16 ,
to lack any
.B 0x
prefix).
It can also be
.BR 0 ,
in which case the number is examined for a leading zero
or a leading
.B 0x
to determine its base.
.PP
The
.I dstlen
parameter of
.I ultot
specifies the size of the
.I dst
parameter;
under no circumstances are more than
.I dstlen
bytes written to
.IR dst .
A result which will not fit is truncated.
.I Dstlen
can be zero, in which case
.I dst
need not be valid and no result is written,
but the return value is unaffected;
in all other cases, the (possibly truncated) result is NUL-terminated.
The
.I freeswan.h
header file defines a constant,
.BR ULTOT_BUF ,
which is the size of a buffer just large enough for worst-case results.
.PP
The
.I format
parameter of
.I ultot
must be one of:
.RS
.IP \fB'o'\fR 4
octal conversion with leading
.B 0
.IP \fB\ 8\fR
octal conversion with no leading
.B 0
.IP \fB'd'\fR
decimal conversion
.IP \fB10\fR
same as
.B d
.IP \fB'x'\fR
hexadecimal conversion, including leading
.B 0x
.IP \fB16\fR
hexadecimal conversion with no leading
.B 0x
.IP \fB17\fR
like
.B 16
except padded on left with
.BR 0 s
to eight digits (full width of a 32-bit number)
.RE
.PP
.I Ttoul
returns NULL for success and
a pointer to a string-literal error message for failure;
see DIAGNOSTICS.
.I Ultot
returns
.B 0
for a failure, and otherwise
returns the size of buffer which would 
be needed to
accommodate the full conversion result, including terminating NUL
(it is the caller's responsibility to check this against the size of
the provided buffer to determine whether truncation has occurred).
.SH SEE ALSO
atol(3), strtoul(3)
.SH DIAGNOSTICS
Fatal errors in
.I ttoul
are:
empty input;
unknown
.IR base ;
non-digit character found;
number too large for an
.BR "unsigned long" .
.PP
Fatal errors in
.I ultot
are:
unknown
.IR format .
.SH HISTORY
Written for the FreeS/WAN project by Henry Spencer.
.SH BUGS
Conversion of
.B 0
with format
.B o
yields
.BR 00 .
.PP
.I Ultot
format
.B 17
is a bit of a kludge.
.PP
The restriction of error reports to literal strings
(so that callers don't need to worry about freeing them or copying them)
does limit the precision of error reporting.
.PP
The error-reporting convention lends itself to slightly obscure code,
because many readers will not think of NULL as signifying success.
A good way to make it clearer is to write something like:
.PP
.RS
.nf
.B "const char *error;"
.sp
.B "error = ttoul( /* ... */ );"
.B "if (error != NULL) {"
.B "        /* something went wrong */"
.fi
.RE